The invention belongs to the technical sector of mechanisms for intervertebral stabilization.
The aim is to link at least two adjacent vertebrae in a manner known per se, to provide spinal stabilization allowing a range of movement between the vertebrae concerned.
Various technical solutions have been proposed to achieve this objective. For example, there is a system consisting of a ligament within a rigid tube arranged between two pedicle screws and attached to the said screws. This rigid tube is placed in compression between the two screws, consequently preventing any movement between the screws and the tube. The result is a rigid assembly generating stresses and strains on the implants with the risks of screws breaking or loosening.
Other systems with stems allow the vertebrae to be brought together, without however permitting any angulation movement between the said vertebrae which move while remaining parallel. The movement resulting from this is not therefore physiological.
According to the patent FR 2.672.202, a surgical implant is known that is composed of pedicle screws, the head of which has at least one radial shoulder defining at least one peripheral area for ligament retention. The link obtained is not sufficiently rigid and does not allow limitation of movement, particularly in extension. Because of this there is excessive demand on the facet joints and reduction in the intervertebral space through which the nerve roots pass. Excessive demand is also made on the disc.
Another solution can be found in patent FR 2.694.182 which describes an attachment for interpedicular prostheses, consisting of a fixation stem with a cylindrical support bearing at its end, a spherical head. A ligament, the ends of which are arranged into loops, connects the spherical heads of two consecutive stems. Before the ligament is fitted to the spherical heads, it may pass through a tightening ring. This solution is not satisfactory and requires complex fitting with the need for a ring to be mounted on the spherical head which is assembled so that it can move on the cylindrical support of the fixation stem. The ring is not adjusted relative to the spherical head. This results in a wide range of movement.
The objective of the invention is to remedy these disadvantages in a simple, safe, effective and rational manner.
The problem that the invention proposes to solve is obtaining stabilization in the context of therapeutic treatment of pathological conditions of the lumbar spine with the objective of conserving the height of the foramen and cohesion of the posterior articular facets and obtaining micromovements between the two instrumented vertebrae.